1. Field of the Invention
Conventional incandescent light sources generally provide radial distribution of light which is used to illuminate a room or the like. However, incandescent light sources consume a lot of power. Replacing incandescent light sources with light emitting diode (LED) light sources improves the power efficiency considerably. Unfortunately, most LEDs emit light into a hemisphere, whereas incandescent light sources are able to provide substantially uniform light emission into an entire sphere. As a result, the mere replacement of incandescent light sources by LED light sources often leads to unsatisfactory and/or insufficient illumination of a space, such as a room.
In addition, conventional incandescent light sources generate a broad spectrum that is experienced as warm white light. LEDs do not generate white lights by themselves. White light may be obtained by using LEDs emitting a short wavelength, e.g. a wavelength between about 420-470 nm, covered with phosphorous material which converts a portion of the emitted light into light having a longer wavelength. The white light produced in this way is often experienced as “cold”. Alternatively, white light may be obtained by using different types of LEDs, each type being suitable for the emission of a wavelength in a different wavelength region. For example, LEDs arranged for emitting blue light may be combined with one or more LEDs arranged for emitting green light and red light. By specific arrangements and the use of optical elements to obtain color mixing white light may be formed. However, it is very difficult to obtain a rather uniform emission of white light over a large solid angle.
Generally, the differences between incandescent light sources and light sources using LEDs described become more noticeable when pluralities LEDs are used in LED light sources. It is extremely difficult to realize a light source using a plurality of LEDs that may act as a point source, particularly if such behavior should coincide with sufficient color mixing.